A study of the metabolism of polyadenylated mRNA is resting and growing lymphocytes revealed the presence of both short-lived and stable molecules. The labile mRNAs do not participate in protein synthesis. Stable molecules are found bound to polysomes or free in the cytoplasm. This system will be used as a model with which to examine the mechanism by which specific mRNAs are selected by the cell for translation. Chemical differences between the labile and stable molecules and the free and bound nRNAs will be investigated. Further studies will encompass normal, resting and growing cells as well as cultured lines of lymphoid origin.